In some hybrid drives for vehicles, an internal combustion engine is combined with at least one electric motor, so that a plurality of drive sources are available for the vehicle. Corresponding to demands made by a vehicle driver, the drive sources can feed their input torques optionally into a drive train of the vehicle. This sometimes produces, depending on concrete driving situations, various drive design possibilities, which serve, e.g., to improve driving convenience and to reduce energy usage, as well as to reduce the emission of pollutants.
Some hybrid drives for vehicles are arranged in serial configurations, parallel configurations or mixed configurations of the combustion engine and electric motors. Depending on the configuration, the electric motors may be switched directly or indirectly into the drive train of the internal combustion engine. For mechanical linkage of the combustion engine and/or electric motors, they may be configured so that they are mechanically linkable with each other via transmissions, for example planetary gears or the like, and clutches.
In order to be able to optimally implement a driver's wish for drive power from the hybrid drive, coordinated actuation of the drive motors of the hybrid drive may be necessary; this may be accomplished by an engine control unit. Actuation of the drive motors may take place on the basis of a setpoint operating state of the hybrid drive to be determined by the engine control unit. The goals in determining this setpoint operating state may be, e.g., low fuel consumption, dynamic driving behavior of the vehicle, and low pollutant emission. A driving behavior of the vehicle is determined decisively here by the dynamic power reserve of the hybrid drive that is available at the setpoint operating states set by the engine control unit. Sometimes, the setpoint operating states may be set by controlling the combustion engine. The additional degree of freedom resulting from the additional electric drive motors is not taken into account here.